Astronomers typically use photons of some sort to figure out what’s happening up there. Sure, some astronomers look for cosmic rays (which are not rays but in fact charged particles like protons), and eventually, gravitational waves are going to be important. But light is the way 99% of astronomy has been done. Now, a new window on the heavens is about to open — and the window goes through the center of the Earth.
The $271 million IceCube project, stuck in the Antarctic ice, would be the largest observatory to use neutrinos — chargeless, high-energy and nearly massless elementary particles. IceCube is a cubic kilometer array consisting of strings of detectors dropped down into ice cores made with hot-water drills. The detectors see the secondary effect of neutrinos colliding with atoms of ice. Neutrinos are terrific for astronomers because, lacking a charge, they aren’t bent by galactic magnetic fields. They may provide some of the only evidence of what happens in the center of supernovae. But they are incredibly elusive — they only rarely interact with matter. Thus the need for a cubic kilometre telescope.
On Saturday, Laura Gladstone of the University of Wisconsin showed that, based on data with only half of the telescope’s 86 strings installed, IceCube was working pretty well: It could see the Moon’s shadow. Common neutrinos particles called muons rain down on Antarctica — some 9 million a lunar month land on IceCube. A much smaller signal was observed when the Moon passed overhead and absorbed some of those muons.
But what Gladstone and her colleagues really want to do is look for the neutrinos that, speeding through the Earth, come up and hit IceCube from underneath. That way, the Earth would blot out most of the common, lower energy muons that fill the galaxy, and instead filter for the zippy high-energy neutrinos that could be coming from pulsars and supernovae, maybe even extragalactic sources. Michael Baker, in the previous talk, said he didn’t quite have the statistics yet to show any point sources in his through-the-Earth looking glass. They’ll have to wait a little longer; IceCube is expected to have all 86 strings installed by 2011.
Image: NSF